1. Field of the Invention
The present invention relates to a method and an apparatus for controlling equalization characteristics of signals reproduced from an optical disk medium.
2. Description of the Related Art
Methods for recording and/or reproducing information on or from an optical disk are in general classified into constant linear velocity (hereinafter, referred to as CLV) schemes and constant angular velocity (hereinafter, referred to as CAV) schemes. If an optical disk having data recorded by the CLV method is played by the same method, the gain of an equalizer for correcting distortions in signals reproduced by a pickup is fixed all the time because the linear velocity of data pits remains constant over all tracks. In contrast, provided that the disk is played by the CAV method, the linear velocity of data pits increases in the radial direction from inner peripheries to outer peripheries, which implies that the frequency characteristics of reproduced signals vary with tracks.
Shown in FIG. 1A is a conventional apparatus for reproducing, at a constant angular velocity, an optical disk 10 with data recorded by the CLV scheme. The apparatus includes a pickup 11 for retrieving information recorded on the optical disk 10 using a laser beam, a sled motor 12a for moving the pickup 11 in the radial direction, a spindle motor 12b for rotating the optical disk 10, a drive unit 30 for driving the sled motor 12a and the spindle motor 12b, a radio frequency (RF) unit 20 for equalizing and shaping signals reproduced from the optical disk 10 by the pickup 11, a servo unit 40 for controlling the drive unit 30 by utilizing focus and tracking error signals obtained from the pickup 11 and for detecting sync signals from the output of the RF unit 20, a digital signal processing unit 50 for retrieving recorded digital data from the output of the RF unit 20, and a microcomputer 60 for supervising the overall operation of the apparatus.
As shown in FIG. 1B, the RF unit 20 further includes an RF summing circuit 21 for summing RF signals created by sub-beams in the pickup 11, an RF equalizer 22 for equalizing signals from the RF summing circuit 21 so that signals created by data pits of various lengths (3T-11T) have the same magnitude, a comparator 23 for generating binary pulse signals by comparing the equalized signals and a slice level, and an integrator 24 for generating the slice level by integrating the binary signals to obtain their average level.
In the above apparatus, given a user""s request to play the optical disk 10, the microcomputer 60 rotationally drives the optical disk 10 at a constant angular velocity, allowing the pickup 11 to retrieve RF signals from the optical disk 10. Signals yielded by two sub-beams in the pickup 11 are added in the RF summing circuit 21 and applied to the equalizer 22, wherein the signals are equalized. The equalizer coefficients which determine the equalizer characteristics are set by the microcomputor 60.
When the optical disk 10 is first accessed, information on the disk is collected and stored in an internal memory (not shown) within microcomputer 60. Referring to the information, the microcomputer 60 determines the radius r, (the distance between the currently accessed track and the center of the disk 10), and examines which region the radius r belongs to from among several regions 1-2, 2-3, 3-4, . . . as shown in FIG. 2. Each region has an associated equalizer gain curve so that a set of equalizer coefficients can be chosen according to the region to which the radius r belongs. For example, if the detected radius r is 2.1, then the equalizer gain curve corresponding to the radius r is B, which indicates that the equalizer gain for 11T signals retrieved from the disk is a.
The microcomputer 60 transmits the chosen set of equalizer coefficients to the RF unit 20 so that the RF equalizer 22 has gain characteristics as shown in the gain curve B. Setting the transmitted coefficients, the RF equalizer 22 equalizes input RF signals with the gain characteristics. The RF equalizer 22 thus controls the gains of frequency sub-bands of reproduced signals, the entire frequency band of the reproduced signal consisting of these sub-bands. The comparator 23 compares the equalized RF signals with a slice level and yields binary signals according to the comparison result. The integrator 24 integrates the binary signals to obtain the average or DC level of the binary signals, wherein the obtained average level is fed back to the comparator 23 as the slice level. The binary signals are processed by the digital signal processing unit 50 and original digital data are finally retrieved.
In the method for adjusting equalization characteristics according to the radius r, the equalizer gain for signals yielded by data pits of the same length on tracks of similar radii may vary depending upon which gain curve is employed. For example, if the radius r is 1.9, the equalizer gain curve A is chosen and the equalizer gain for 11T signals is b (as shown in FIG. 2). Compared to the previous example wherein the equalizer gain for the same signals is a, there is a fairly big difference in the equalizer gain despite the fact that the two radii are similar. The discontinuity in the equalizer gains remarkably increases around the boundary of two regions partitioned by the radius r.
In addition, the relation between the radius and appropriate equalizer gain characteristics varies with disk types and disk makers. Considering this fact, therefore, the RF equalizer intended for improving signal qualities might distort reproduced signals if the RF equalizer coefficients are adjusted inappropriately.
Accordingly, the present invention is directed to a method and apparatus for adjusting equalization characteristics of signals reproduced from an optical disk that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The present invention is also directed to a method and an apparatus for adjusting equalization characteristics of signals reproduced from an optical disk with varying linear velocities of tracks.
In accordance with the purpose of the invention, as embodied and broadly described, one aspect of the invention includes a method for adjusting equalization characteristics of signals reproduced from an optical disk medium, including detecting a linear velocity of a track on a rotating optical disk medium, and controlling equalization characteristics of signals reproduced from the track based on the detected linear velocity.
In another aspect, the invention includes an apparatus for adjusting equalization characteristics of signals reproduced from an optical disk medium, including a detector to detect a predetermined signal derived from a track of the optical disk medium and to output detection signals when the predetermined signal is detected, a device to generate an output signal representing a linear velocity of the track based on the detection signals, and a controller to control equalization characteristics for reproduced signals based on the output signal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention.